Heat treatment furnace

ABSTRACT

A furnace for the heat treatment, particularly enamel firing, of small mechanical components. The furnace comprises a block of thermal insulation material in which a well is formed. A heat source, such as a gas burner, is accommodated within the well and a hearth plate extends across the top of the well, being mounted on the block by spaced legs. Removably mounted over the hearth plate is a bell-shaped cover of transparent refractory glass, the cover having an opening in its upper region for the escape of hot gasses from the cover after having risen from the burner through the spaces between the legs.

United States Patent [72] Inventor JeanAndreu Rhone, France [2]] Appl. No. 36,615

[22] Filed May 12, 1970 [45] Patented Oct. 5, 1971 [73] Assignee Application Des Gaz Paris, France [32] Priority June 30, 1969 [33] France [54] HEAT TREATMENT FURNACE 11 Claims, 9 Drawing Figs.

[52] US. Cl 263/40 R,

263/2 R [51] Int. Cl F271) 3/02 [50] Field of Search 263/1, 2 R,

4, 5 R, 40 R, 41, 42 R, 43; 126/274 [56] References Cited UNITED STATES PATENTS 2,210,301 8/1940 Newby 263/43 X 2,943,557 7/1960 Suehlsen 126/274 X Primary Examiner.lohn J. Camby Att0rney-Alexander & Dowell ABSTRACT: A furnace for the heat treatment, particularly enamel firing, of small mechanical components. The furnace comprises a block of thermal insulation material in which a well is formed. A heat source, such as a gas burner, is accommodated within the well and a hearth plate extends across the top of the well, being mounted on the block by spaced legs. Removably mounted over the hearth plate is a bell-shaped cover of transparent refractory glass, the cover having an opening in its upper region for the escape of hot gasses from the cover after having risen from the burner through the spaces between the legs.

PATENTED um 5 ml 3; 6 1. 0 597 SHEEI 2 0F 2 I; INVENTOR.

HEAT TREATMENT FURNACE The present invention concerns heat-treatment furnaces, particularly such furnaces intended for the firing of enamels particularly of mechanical parts of small dimensions.

An object of the present invention is to improve a furnace of this type so that the losses of heat by radiation, conduction and convection are very low, while being simple to construct, resistant to wear and easy to maintain in use.

The'fumace constructed in accordance with the present invention comprises a hearth covered by a removable transparent bell shaped cover of refractory glass, characterized in that the hearth is formed by a plate covering, on a block of heat-insulating refractory material, a well coaxial to the cover, in which a heat source is provided.

The aforementioned well is preferably enlarged so as to form round the heat source a reflector capable of transmitting, below the hearth plate, the portion of heat radiation emanating from the heat source, downwardly and towards the periphery.

In a preferred embodiment, the heat source is formed by a gas burner, the hearth plate resting by its periphery on the refractory block by means of feet, has between these feet, hollowed out portions through which the hot gases rising in the well and diverging below the plate can escape upwardly, and the cover is provided at the top with an opening for the evacuation of combusted gases.

The block of refractory material is preferably made of a felt of slightly compressed mineral fibers.

The hearth plate is preferably made of refractory metal, particularly of stainless steel.

The opening provided at the top of the bell-shaped cover is preferably formed so that its edge is turned upwardly and outwardly in such manner as to form an external peripheral throat in which a loop of relatively rigid wire is engaged, said loop being extended by armswhich are pivoted on the base of the apparatus so that it is possible to raise the cover at any moment without having to grip it directly.

The burner is preferably formed by a hollow cylinder covered with a metal gauze or perforated sheet and connected at its lower end to a housing secured below the base of the apparatus to form a chamber for the mixing of the gas emanating from a suitable nozzle, with the external air moved by the gas jet, in known manner. The connection of the housing below the base is preferably effected by a perforated clip which engages round the nozzle and by means of a lug opposed to the aforementioned clip and secured to the base by a single screw.

The base itself is preferably hollow, the shaft of the arms supporting the cover being hinged to the sidewalls thereof, while the arms themselves pass through slits formed in the upper wall thereof.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

FIG. I is a general longitudinal section through a gas furnace according to the invention;

FIG. 2 is a plan view thereof, the cover being assumed to be removed and the arms supporting it being partly broken away;

FIG. 3 is a section through a detail showing the manner of assembly of the two shells forming the base;

FIG. 4 is an underside plan of a burner for the furnace, said burner being assumed isolated;

FIG. 5 is an end view in the direction of arrow V of FIG. 4;

FlGr6is a section taken on the line VI-VI of FIG. 4;

FIG. 7 is a plan view of the arms for supporting a cover of the furnace;

FIG. 8 is an elevational view of an operating knob of the arms shown in FIG. 7; and

FIG. 9 is a section taken on the line IXIX of FIG. 8.

The furnace shown in FIGS. 1 and 2 comprises a hollow base I which is formed by two opposing shells 2 and 3 suitably assembled together to form top and bottom members in the manner of a box and lid, this assembly being ensured by a number of ribs 4, one of which is shown in FIG. 3. As shown,

the upper part of each rib 4 comprises a threaded portion 4a for receiving a screw 5 located in a depression in the wall surface 2a of the shell 2 to connect the latter to the rib. The lower end of the rib extends in the form of a threaded stem 4b of small diameter which passes through the bottom 3a of the shell 3 to screw into a lock nut 6 embedded in the material of a truncated foot 7, of plastic material, for example. Naturally, to permit a tight connection to be obtained between the lock nuts 6 and the feet 7, the lock nuts are formed in known manner with peripheral notches (not shown).

Located within the base 1 is a block 8 formed of refractory material, preferably of felt, of compressed mineral fibers. The center region the block 8 is hollowed out to form a well having a truncated section, the small end of which extends downwardly and is connected to a cylindrical bore 8b communicating with the lower face of the block. The latter rests on three projections 3b upstanding from the bottom 30 of the lower shell'3. The block 8 also comprises an upper circular edge 8c encircling the large end of the well 84 and is covered by a protecting metal layer 9. The cover 9 includes an outwardly projecting portion 9a which engages with the surface 2a of shell 2. The upper surface 20 of the shell 2 is perforated for the passage of the edge 8c of block 8, the resultant opening being defined by a circular projection 2b, the turned-down inner edge of which straddles the projecting part 9a of the cover 9, thus ensuring correct positioning of the block 8.

The edge 8c and the cover 9 disposed over it comprise on the periphery three depressions in which are located three feet 10a extending radially from a circular plate or hearth T0, the diameter of which is less than that of the large end of the well 8a. The plate 10 may be made, for example, of heat-resistant stainless steel.

Disposed on the bottom 31; of the lower shell 3 is a housing 11 (see also FIGS. 4-6) having a plan outline in the form of an arc of a little more than 180 connected to two converging tangents, the latter stopping however before the point of convergence so as to form a rectangular opening lla (FIG. 6) at one of the ends of the housing 11. In the embodiment shown, the housing is formed by a lower pressed portion to which a cover is attached by crimping. This cover or upper end of the housing 11 is concentrically perforated by a circular opening in the plane section of the housing and in its perforated opening a tube 12 is connected by crimping, the tube 12 extending upwardly through the bore 8b of block 8 to terminate above the bore 8b in a head 13 made of metal gauze. The upper end of the housing 11 is connected by welding or the like to a lug 11b displaceably mounted on the bottom of the shell 3 by a screw 14 secured in a locknut 15 connected to the bottom. Alternatively a self-tapping screw 14 may be used, that is to say, capable of providing its own thread in a metal sheet perforated with a bore of suitable diameter, thus making it possible to dispense with the locknut 15. As shown in FIG. 4, the lug 11b is located on the housing opposite the inlet 11a. The upper end of the housing 11 is provided with another lug 11c extending through the opening 11a, then is bent at an angle of and provided with an opening lld (FIG. 5) in which a gas jet nozzle 16 is engaged (FIG. 1) and which is secured by a locknut 17 to a perforated clip 18 welded below the bottom 30 of the shell 3, this locknut being connected to a tube 19 capable of receiving a flexible supply line such as indicated by broken lines 20.

The lower edge of a bell-shaped cover 21, made of refractory glass, normally rests on the above-described cover 9 In its upper portion, the cover 21 is provided with an aperture 21a, the edge of which is turned upwardly and outwardly in such a manner as to form a throat adapted to receive a loop 22a made of a wire having a diameter sufficient to ensure the required rigidity. As shown in FIG. 7, the loop 22a is eonnected to two parallel arms 22b which are curved downwardly, (see FIG. I), then pass through two slots 2d (FIG. 2) formed in the surface 2a of the shell 2, are then bent with an angle of 90 in opposite directions to form together a pivotal axle passing through the sidewalls of the base 1. To

strengthen the pivotal axle thus obtained, the two 90 elbow bends mentioned above and the adjacent straight portions are clamped between the two thicknesses of a rectangular sheet 23 folded back over itself, these two thicknesses being provided with suitable impressed locating means to ensure centering, being traversed by a locking rivet 24.

One of the ends of the aforementioned pivotal axle is bent at an angle of 90 as shown at 22d in FIG. 7, to receive an operating knob 25 (FIGS. 8 and 9). As shown, the knob 25 is shaped in such manner as to be force-fitted on the curved end 22d in order to allow movement of the arm 22b. For this purpose, it is provided with a blind bore 250 at the end which is connected to one of the sides by a notch 25b. In order to position the knob 25, it is forced on the curved end 22d until the adjacent straight part 221. engages in the notch 25b.

The operation is as follows: since the tube 19 is connected to a source of pressurized gas, for example, to a tank of liquified butane, the jet issuing from the nozzle 16 penetrates into the inlet Ila of the housing 11 driving with it a large proportion of external air. The mixture gradually loses speed as it advances in the diverging part of the housing and reaches the substantially tranquil condition below the tube 12. It rises in this tube to pass through the head 13 above which it is ignited. The resultant flame heats the hearth plate 10, the gasses escaping through the annular space formed between this plate and the upper edge of the well 80 whence it rises in the cover 21 to be evacuated through the aperture 21a. Due to the strongly insulating character of the material forming the block 8 in which the well is formed, losses by conduction are very small.

When the required temperature is reached, the cover 21 is raised by means of the knob 25 to bring the cover to the position shown in broken lines in FIG. 1. The articles which it is desired to treat, and particularly enamels to be tired are placed on the hearth plate 10. The cover 21 is returned to the base 1 and the apparatus is operated, observation being kept, through the cover 21, of the appearance of the treated articles to decide when the treatment is finished.

In a preferred embodiment, the inlet 11a is dimensioned in cross section and in extent relatively to the nozzle 16 so that the housing 11 received practically all the air required for combustion. But it is also possible for the additional air to reach the burner through the clearance between the bore 8b and the tube 12 (it being understood that in this case the bottom 3a of the lower part 3 should be suitably perforated to facilitate the flow of air into the base).

The furnace of the present invention permits the articles being treated to be observed from all angles contrary to conventional apparatus having an observation window of small area. Due to the presence of the refractory well which encloses the burner and the thin mass of the plate or hearth 10, the temperature is adjusted extremely rapidly; in a furnace for enamel, the duration for achieving this correct temperature may be of the order of only a few minutes. Access to the treated articles is extremely easy, since it is only necessary to turn the knob 25 to uncover them completely over the entire circumference of the plate 10. The burner is instantly removable by simply undoing the screw 14 (and, if necessary, the locknut 18, if the clearance between the pipe 12 and the bore 8b is not sufficient to disengage the housing 1 1c from the nozzle 16). The entire unit is made with a minimum of parts which are extremely economical to manufacture.

It should also be understood that the foregoing description is given only by way of example and in no way limits the scope of the present invention which would include the replacement of the details of construction which have been described, by any other equivalent details. Thus, for example, the wire gauze forming the head 13 of the burner could be replaced by a perforated sheet or even, if desired, be purely and simply omitted. Likewise, each of the ribs 4 need not have a threaded extension 4b for screwing into the foot 7, but may be pierced with a threaded bore to receive a threaded stem connected to the foot.

We claim: l. A heat treatment furnace, particularly for the finng of enamels, comprising a block of thermal insulation material having a well fonned therein, a hearth in the form of a plate mounted on said block so as to extend across a top opening of the well, a heat source provided in the well, and a bellshaped cover transparent refractory glass removably mounted over said hearth.

2. A furnace according to claim I, wherein the well in the block of refractory material is so shaped as to form, around the heat source, a reflector capable of redirecting, towards the hearth plate, at least a portion of any heat emanating from the heat source and radiated downwardly and towards the periphery of the well.

3. A furnace according to claim 1, wherein the heat source is a gas burner, the hearth plate is supported across the top opening of the well a plurality of feet engaging with the insulation block in such a manner as to form, between these feet, apertures through which hot gases rising in the well and diverging under the hearth plate can escape upwardly into the cover which has in its top region, an opening for the escape of combustion products,

4. A furnace according to claim I, wherein the block of refractory material is a felt of slightly compressed mineral fibers 5. A furnace according to claim 1, wherein the hearth plate is formed of refractory stainless steel.

6. A furnace according to claim 3, wherein the opening in the cover for the escape of combustion products is bent upwardly and outwardly to form an external peripheral throat in which a wire loop engages, said loop being extended to form arms which are pivotally mounted on a base of the furnace, whereby the cover may be raised and lowered about said pivotal mounting.

7. A furnace according to claim 3, wherein the burner is formed by a hollow cylinder having its upper end covered by a wire gauze sheet and being connected at its lower end to a housing forming a mixing chamber for the gas and air.

8. A furnace according to claim 7, wherein said housing is secured to a base of the furnace by a preferred clip which engages round a gas nozzle, and by means of a lug opposed to said clip and which is secured to the base by at least one screw.

9. A furnace according to claim 6, wherein the base is formed by means of two shells secured together to form a hollow housing in the manner of a box and its lid, the arms carrying the cover being pivoted on the sidewalls of the base and extending through slots formed in an upper surface of the base.

10. A furnace according to claim 9, wherein the shells forming the base are secured together by intermediary n'bs, the upper end of each rib being secured to the upper shell by means of a screw, while the lower end of each rib is secured to the lower shell by means of a threaded stem connected to the rib and which cooperates with a threaded bore provided in a foot arranged below the lower shell.

' 11. A furnace according to claim 9, wherein the shells forming the base are secured together by intermediary ribs, the upper end of each rib being secured to the upper shell by means of a screw, while the lower end of each rib is secured to the lower shell by means of a threaded stem connected to a foot disposed below the lower shell and which cooperates with a threaded bore provided in the rib. 

1. A heat treatment furnace, particularly for the firing of enamels, comprising a block of thermal insulation material having a well formed therein, a hearth in the form of a plate mounted on said block so as to extend across a top opening of the well, a heat source provided in the well, and a bellshaped cover transparent refractory glass removably mounted over said hearth.
 2. A furnace according to claim 1, wherein the well in the block of refractory material is so shaped as to form, around the heat source, a reflector capable of redirecting, towards the hearth plate, at least a portion of any heat emanating from the heat source and radiated downwardly and towards the periphery of the well.
 3. A furnace according to claim 1, wherein the heat source is a gas burner, the hearth plate is supported across the top opening of the well a plurality of feet engaging with the insulation block in such a manner as to form, between these feet, apertures through which hot gases rising in the well and diverging under the hearth plate can escape upwardly into the cover which has in its top region, an opening for the escape of combustion products,
 4. A furnace according to claim 1, wherein the block of refractory material is a felt of slightly compressed mineral fibers
 5. A furnace according to claim 1, wherein the hearth plate is formed of refractory stainless steel.
 6. A furnace according to claim 3, wherein the opening in the cover for the escape of combustion products is bent upwardly and outwardly to form an external peripheral throat in which a wire loop engages, said loop being extended to form arms which are pivotally mounted on a base of the furnace, whereby the cover may be raised and lowered about said pivotal mounting.
 7. A furnace according to claim 3, wherein the burner is formed by a hollow cylinder having its upper end covered by a wire gauze sheet and being connected at its lower end to a housing forming a mixing chamber for the gAs and air.
 8. A furnace according to claim 7, wherein said housing is secured to a base of the furnace by a preferred clip which engages round a gas nozzle, and by means of a lug opposed to said clip and which is secured to the base by at least one screw.
 9. A furnace according to claim 6, wherein the base is formed by means of two shells secured together to form a hollow housing in the manner of a box and its lid, the arms carrying the cover being pivoted on the sidewalls of the base and extending through slots formed in an upper surface of the base.
 10. A furnace according to claim 9, wherein the shells forming the base are secured together by intermediary ribs, the upper end of each rib being secured to the upper shell by means of a screw, while the lower end of each rib is secured to the lower shell by means of a threaded stem connected to the rib and which cooperates with a threaded bore provided in a foot arranged below the lower shell.
 11. A furnace according to claim 9, wherein the shells forming the base are secured together by intermediary ribs, the upper end of each rib being secured to the upper shell by means of a screw, while the lower end of each rib is secured to the lower shell by means of a threaded stem connected to a foot disposed below the lower shell and which cooperates with a threaded bore provided in the rib. 